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1. Which part of the following problem should be worked first?
111+33+87/5=135

A. 111+33
B. 33/5
C. 87/5
D. 33+87***

2. A student solves the following problem: 2(x-3)+3x=19
Step 1 2x=6+3x=19
Step 2 (2x+3x)-6=19
Step 3 5x-6=19
Step 4 5x-6+6=19+6
Step 5 5x=25
Step 6 x=5

What property justifies step 4?
A. addition property of equality
B. Communitive property of addition
C. Substitution***
D. Multiplication property of equality